Radiological imaging is recognized to have significant value for the dental practitioner, helping to identify various problems and to validate other measurements and observations related to the patient's teeth and supporting structures. Among x-ray systems with particular promise for improving dental care is the extra-oral imaging apparatus that is capable of obtaining one or more radiographic images in a series and, where multiple images of the patient are acquired at different angles, combining these images to obtain a contiguous panoramic radiograph of the patient showing the entire dentition of the jaw, a tomographic image that contains more depth detail, or a computerized tomography (CT) volume image. To obtain images of any of these types, a radiation source and an imaging detector, maintained at a fixed distance from each other, synchronously revolve about the patient over a range of angles, taking a series of images by directing and detecting radiation that is directed through the patient at different angles of revolution.
Combination systems that provide both CT and panoramic x-ray imaging can include an X-ray source, an X-ray detector for detecting X-rays having passed through the subject, and supporting means for supporting the X-ray source and the X-ray detector so that they are spatially opposed to each other across the subject; and mode switching means for switching between a CT mode and a panorama mode. To detect X-rays, only one large area X-ray detector is used. The X-ray imaging apparatus can obtain both types of images by switching modes during the imaging session. However, the proposed imaging apparatus performs both CT and panoramic imaging using only one detector. This requires an expensive detector capable of carrying out both imaging functions in a satisfactory manner.
A combination imaging system can provide both CT and panoramic imaging using two separate sensors or detectors. By way of example, FIG. 1 in the present application shows a combined panoramic and CT imaging apparatus 40. A telescopic column 18 is adjustable for height of the subject. The patient 12 or other subject, shown in dotted outline, is positioned between an x-ray source 10 and an x-ray imaging sensor panel 20. X-ray imaging sensor panel 20 rotates on a rotatable mount 30 in order to position either a CT or a panoramic sensor 21 for obtaining the exposure. For CT imaging, CT sensor 21 is positioned behind the subject, relative to x-ray source 10. The operator rotates CT sensor 21 into this position as part of imaging setup. Similarly, the operator rotates panoramic sensor 21 into position behind the subject as part of the setup for a panoramic imaging session.
Another recent imaging system combines CT, panoramic, and cephalometric imaging from a single apparatus. For example, commonly assigned U.S. Patent Application Publication No. 2012/0039436 entitled “COMBINED PANORAMIC AND COMPUTED TOMOGRAPHY APPARATUS” to Bothorel et al. describes such a system.
A computerized tomography (CT) imaging apparatus operates by acquiring multiple 2D images with a rotating imaging ensemble or gantry that has an x-ray source and, corresponding to (e.g., opposite) the x-ray source, an imaging sensor having a selectable spatial relationship (e.g., rotating about a fixed axis) relative to the patient. CT imaging allows the reconstruction of 3D or volume images of anatomical structures of the patient and is acknowledged to be of particular value for obtaining useful information for assisting diagnosis and treatment.
Conventional digital radiography detectors have some limitations related to how attenuation of radiation energy at a single exposure is interpreted. For example, it can be very difficult, from a single exposure, to distinguish whether an imaged object has a given thickness or a given attenuation coefficient. To resolve this ambiguity, some systems provide separate, sequential low-energy and higher energy exposures and use the resulting difference in image information to distinguish between types of materials. However, in order to provide this information, this type of imaging requires that the patient be subjected to additional radiation for the second exposure. This problem can be compounded for CT imaging, in which multiple images are obtained, one from each of a number of angles of revolution about the patient.
Conventional CT imaging provides useful information that aids in diagnosis and treatment, but is constrained by limitations of the imaging sensor apparatus itself, and there are concerns over exposure levels needed for obtaining the desired image quality. There is room for improvement in system performance and in providing types of imaging that address practitioner interests with respect to a particular patient. Improvements are also needed for more accurate equipment positioning relative to the patient as well as for overall patient comfort. Additional improvements in image acquisition sequences and processing are also desired.